FS#1099 - Swiftdove-UXP theme for Icedove-UXP

Description:Historically, Swiftdove was a Thunderbird-based application built on XUL platform around 2007 and abandoned in 2010. It was optimized for several architectures using the following methods such as the Profile-Guided Optimization (PGO) and binary code optimization for computers with limited resources.

Since FossaMail may potentially be revived on UXP in the future [0] and Swiftdove contains non-trademarked graphics and logos, we could port Swiftdove to UXP platform as theme for Icedove-UXP.